A chemical added to the mix of rubber, fillers, sulphur, zinc oxide etc., to speed up the vulcanization process.

A chemical added to the mix of rubber, fillers etc. to ‘kick off’ the vulcanization process.

A general word for antioxidants and antiozonants.

A chemical present in the compound and vulcanizate that will slow down the rate of oxidative degradation. It interferes with the chain of chemical reactions that cause degradation and must therefore be intimately dispersed throughout the mix. It has essentially no effect on degradation by ozone

A chemical present in the compound and vulcanizate that will slow down or halt degradation by ozone. Antiozonants function by migrating to the surface of the vulcanized rubber product and then, either without chemical reaction (waxes) or after reaction with ozone, form an ozone-impermeable barrier or skin on the rubber surface. If the skin is cracked by abrasion, flexing or cleaning degradation will occur until the antiozonant has migrated from the bulk of the product to repair the damage. They offer little or no protection against oxidative degradation.

The smallest unit an element can be divided into and still retain the unique identity of that element. Atoms can be further split into a number of sub-atomic particles but these are common to all elements. It is the particular combination of sub-atomic particles that defines each element.

When two carbon atoms in a molecule are joined by a double (C=C), rather than a single (C-C) bond, the OLEFINIC or ‘ENE’ linkage has two important properties. Firstly, the remaining two bonds from each carbon atom lie in the same plane ( >C=C< ) and secondly, the bond is rigid so the carbon atoms cannot rotate relative to each other. In a polymer chain one of each of the ‘free’ carbon bonds will form part of the chain whilst the others will be attached to a hydrogen or other relatively small atom or group of atoms. If the two polymer chain fragments are on the same side of the double bond (i.e. both above or both below in the illustration above) then the bond is called a CIS bond or CIS linkage. If they are on opposite sides (one above and one below) it is TRANS. This can have a substantial effect on the properties of the polymer. For instance, natural rubber has an ‘all CIS’ configuration whilst gutta percha has an identical chemical composition but the isoprene molecule is in the ‘all TRANS’ configuration.

A mixture of rubber and all the additives which will be in the final vulcanized product but before heat is applied to effect the cure.

The CURING process was so named by Charles Goodyear when he discovered that a mixture of natural rubber, white lead and sulphur, when heated, cured rubber of its two main commercial disadvantages, it turned sticky when hot and turned brittle when cold. It also prevented or delayed putrefaction. Hancock, in the UK, called the process VULCANIZATION after a suggestion by Mr Brockedon. Today the term ‘VULCANIZATION’ is restricted to sulphur cures of elastomers whilst the term ‘CURING’ is applied to any process where a three dimensional network is built up from polymer chains.

This term is used to describe any rubber or rubber-like material.

Extending oils can be added to elastomers to soften them. Manufacturers are always balancing cost against performance and it is possible to take an elastomer, add considerable amounts of (cheap) filler, which makes the product hard, and then soften it down with (cheap) oil. Performance acceptable, price less or margin more!

Inorganic materials such as calcium carbonate (whiting) and clay, as well as carbon black, which are added to plastics and elastomers to ‘bulk them out’. A few fillers such as carbon black interact with the elastomers to give a mixture which has more strength than would be expected and these are called reinforcing fillers.

A number of atoms (2 or more) joined together in a particular way to uniquely define a chemical moiety. For instance, 2 carbon atoms, 6 hydrogen atoms and 1 oxygen atom can be joined in the order CH3-CH2-OH (ethyl alcohol) but also as CH3-O-CH3 (dimethyl ether).

A small molecule which is the basic ‘building block’ of a polymer chain.

Latex can be vulcanized over a period of several hours by the addition of the usual ingredients – sulphur, zinc oxide and an accelerator – to the warm latex. Visually the vulcanized latex appeared indistinguishable from the untreated material but when it was coagulated and/or dried it behaved as if vulcanized. The procedure of treating the latex in this way is called pre-vulcanization and any further short heating period after coagulation, post-vulcanization.

Some plastic materials are quite hard and non-elastic. However, when an appropriate solvent is added the resulting material takes on rubber-like properties. The solvent is called a plasticizer.

A nominally linear chain (but often with some branching) of many hundreds or thousands of one specific monomer. Written as (monomer)n. Thus the monomer ethylene (C2H4) becomes polyethylene (polythene) (C2H4)n. Natural rubber is a homopolymer with the chemical structure (C5H8)n.

If two different monomers are mixed together before being polymerized the chain will have the different monomers distributed randomly along its length. This is a copolymer. If butadiene and styrene are co-polymerized the result is styrene butadiene rubber (SBR).

Sometimes individual monomers may be polymerised to form short chains and then these chains mixed and further polymerised so that the final polymer has a ‘blocky’, rather than random distribution. If styrene and butadiene are polymerised in this way, the rubber produced is called styrene butadiene styrene rubber (SBS). This technique can also be used to prepare branched chains and ultimately ‘STAR COPOLYMERS’ of styrene.

If three monomers are mixed, the resulting polymer is a terpolymer. The copolymerisation of ethylene and propylene gives ethylene propylene rubber (EPR) but this has no residual double bonds where crosslinking can occur. The addition of a third monomer, at a low level of 3 to5%, gives the terpolymer EPDM which can be crosslinked.

An addition polymer is one resulting from the joining together of its monomers without the loss of any components of the monomers i.e. n monomers of C2H4 go to (C2H4)n.

Some polymers have a regular A-B-A-B-A structure where ‘A’ is a monomer with two (or more) functional groups and ‘B’ is another monomer with two (or more) complementary functional groups. ‘A’ and ‘B’ react together with the elimination of a small molecule such as water from each complementary pair of groups. The elimination of water was noted in some early investigations of this chemistry and led to the name ‘condensation’ for this general type of reaction.

‘Rubbery’ polymers are defined as those materials which can be crosslinked to provide a three dimensional network and yet still retain a high extensibility coupled with an ability to recover quickly their original shape – what is generally called their elastic property.

Describes those polymers which retain a high extensibility coupled with an ability to recover quickly their original shape but are not crosslinked.

See CIS/TRANS above.

See CURING & vulcanization and PRE- & POST-VULCANIZATION above.